Separation of butenes, nu-butane, c-3 and lighter hydrocarbons by extractive distillation



Feb. 18, 1947. Q R WAGNER 2,415,921 SEPARATION OF BU'I'ENES, rbBUTANE, e s AND LIGHTER awnocnaons BY EXTRACTIVE DISTILLATION Filed Feb. 10. 1944 FEED (C TCONTENT ACCUMULATOR OF IST 5 AGE DEHYDR ENATON EFFLUENT NISUIRENE zecesze 111i: L E I 2 u STORAGE WAT R m cm W LAYE E 5 as 2 J 1 I0 A a TO END STAGE g E DEHYDRO- a 9 m GENATION uwn' L. BU TENES) WATER INVENTOR C. F!v WAGN ER Patented Feb. 18, 1947 SEPARATION OF BUTENES. N-BUTANE, -3

AND LIGHTER HYDROCARBONS BY Ex- TRACTIVE DISTILLATION Gary R. Wagner, Utlca, Ohio, assignor to Ph llips Petroleum Company, a corporation of Delaware Application February 10, 1944, Serial No. 521,836

3 Claims. (Cl. 202-395) This invention relates to a method for separation and recovery of C4 hydrocarbons from a complex hydrocarbon mixture comprising both normally gaseous and normally liquid hydrocarbons heavier hydrocarbons. This separation is accomplished by liquid-vapor contacting of the hydrocarbon mixture with a selective solvent in an extractive distillation unit, absorber 2. This absorber is a tower, the upper section of which acts 2 as an absorber for the normal butenes using a relatively non-volatile solvent introduced at the top of the absorber, 2, through line III. For the purpose of discussing my invention, furfurai conof both saturated and unsaturated linkages. 5 taining a small amount oi. dissolved water has More specifically, this invention relates to the been selected as an example from the group of preparation of a satisfactory normal butene feed various solvents available. Various other solvents stock to be catalytically dehydrogenated to butathat will meet the practical requirements for C4 diene. This invention further relates to a process hydrocarbon separations by solvent extraction wherein a n-butane-butene-l-butenes-2 (both are disclosed in co-pending application, Serial No. low and high boiling) mixture, such as that ob- 454,312 filed August 10, 1942. The bottom sectained from first stage dehydrogenation of n-bution oi tower 2 acts as a stripper to remove ntane in a two step dehydrogenation process for butane which is absorbed to some extent in the top manufacture or butadiene, is charged to a seiecsection of the tower. The reboiling of the solvent tive solvent extractive distillation unit wherein at the bottom of the tower furnishes the necessaid n-butane is recovered as a separate product sary vapors to carry out this stripping while reand recycled to first stage dehydrogenation and turning part of the overhead product 3 as reflux the butene-1 and butenes-2 (both low and high to the top of the tower by line 5 serves to remove boiling) are recovered as a combined product and the heat added by the reboiler. The overhead charged to second stage dehydrogenation for product 3 comprising mainly n-butane with subconversion to butadiene. stantialiy all 01' any C3 and lighter hydrocarbons The object oi my invention is to prepare a satisintroduced in the feed is condensed and introfactory butene feed stock for second stage dehyduced into reflux accumulator 4. A portion of the drogenation. Another object or my invention is lighter hydrocarbons are bled of! from accumuthe separation of a complex hydrocarbon mixture 5 lator l in order to reduce pressure in the system. in order to recover n-butane of suitable purity These lighter hydrocarbons are recycled via line I and concentration for recycle to first stage deto a vapor recovery unit (not shown). A n-buhydrogenation and also to recover a combined tane-rich hydrocarbon stream is removed from butenes product of suitable concentration and the bottom of reflux accumulator 4, a portion of purity to be used in second stage dehydrogenathis n-butane-rlch stream is returned as reflux tion by charging a complex C4 hydrocarbon mixto the top of the absorber 2 through line 5, the ture to a selective solvent extractive distillation rest of said n-butane rich stream being recycled to first stage dehydrogenation or to butane stor- This extractive distillation process using a seage by means oi line 6. V lective solvent is advantageous since it makes The furtural solvent containing in solution the Po e e Sep o and recovery of n-butane normal butenes as well as any isobutylene presstock for recycle t0 st st e dehydro ent is withdrawn from the bottom of absorber 2 simultaneously with the preparation of a comthrough line 8. This butenes-rich solvent on leavbined normal butene feed stock for charging t0 ing the bottom of absorber 2 is passed to a solvent a Seco d stage dehydrogenation un t. stripper 9 where the combined butenes are re- The accompanying drawing schematically illusmoved overhead through line H while the lean or trates my invention and shows the distribution of denuded solvent is returned after suitable cooling the principal hydrocarbons. i to the top of absorber 2 through line [0. In order In accordance with my invention the n-butane to keep from using excessive temperatures on and the combined normal butenes are recovered the reboiler of the stripping tower 9, water is inas the finished products from separation of a comtroduced through line i5 to the bottom of stripper pl x hydro r n i r comprising principally 9 where it is vaporized and furnishes part 01' the C4 hydrocarbons. In addition this mixture may necessary stripping vapor. The water going overcontain small amounts of hydrogen, methane, head with the butenes product is condensed and ethane, ethylene, propane, propylene, C5 and returned to the reboiler thereby being maintained in a short closed cycle. The butenes thus stripped from the furfural are passed overhead through line ll, condensed and passed to accumulator I! wherein the condensate is separated into two layers. one of water which is withdrawn and recycled to stripper 9 via line i 6, and the other of the combined normal butenes which are withdrawn via line H. Part of the combined butenes are returned through line 13 to the top of the stripping tower 9 as reflux, the remainder of the combined butenes are charged as feed stock to a second stage dehydrogenation unit (not shown) for conversion to butadiene.

Example In actual operation oi first stage dehydrogenation of iii-butane, a roughly stabilized C4 hydrocarbon mixture was introduced to the furfural absorber 2 through line I. This C4 rich feed This i'eed stock was introduced into a 100 plate bubble tray absorber 2 through line I, at the center or the column. Furiural containing a small percentage of water and traces of hydrocarbon was introduced into absorber 2 near the top 01' the absorber through line ill. The mol ratio of the furiural introduced near the top of the column to the quantity of hydrocarbon feed to the tower was about 34.2: 1. The hydrocarbon reflux ratio based on hydrocarbon feed was about 5.39:1. The average tower operating pressure was '75 pounds per square inch absolute, the top temperature was 110 F. and the bottom temperature was 285' F. The overhead vapors withdrawn through line 9 were condensed and collected in reflux accumulator 4. This overhead vapor stream 3 had the following composition:

Stream 3, Component moi per cent and lighter 4. l8 Isobutylono 03 Bu c-l 2.78 n-Bu 93. 01

Some of the lighter hydrocarbons were drawn of! from the reflux accumulator 4 through line I. This stream, which was recycled to a vapor recovery unit, had the following composition:

Stream 7,

component moi per cent 0 and lighter Butcne- A n-butane-rich hydrocarbon stream was withdrawn from the bottom of reflux accumulator l and divided, the larger part of this stream was returned as reflux to the top of the absorber 2 through line 5', the rest or the n-butane-rich stream was recycled to a first stage dehydrogenation unit through line 9 for conversion to butenes; This n-butane-rich hydrocarbon stream had the following composition:

Component r n ol r r c x it C; and lighter 4. i4 lsobutylena U3 Butene-l 2.11 n-Butane 93.06

The composition of the product withdrawn from the bottom of absorber 2 through line 8 wasasfollows:

sass.

Butadieue Trace Isobutylene (l3 Butane-l 74 Butane-2 (low boiling). .44 Butane-2 (high boiling) .32 n-Butane 04 Cl and heavier Trace Furiural 9B. 43

This butenes-rich furiural stream from the bottom of absorber 2 was introduced into stripper 9, a 20 tra iractionator, through line 9. The stripper 9 was operated with a reflux of 6.7:1, average pressure of 65 pounds per square inch absolute, top temperature of 126 F. and bottom temperature of 302 F. The lean iurtural containing a small percentage of water was with; drawn through line It. This lean iurfural stream had the following composition:

Stream 10, Component moi per cent Butadiene Trace Isohutylene 'ira Butane-l .05 Butane-2 (low-boiling) 03 Butane-2 (high boiling) .02 n-Butane Trace Furiurai (with a small percentage of water) 99.

The overhead product from stripper 9 consisting principally of butenes and vaporized water was withdrawn through line H, condensed and introduced into accumulator i2. The hydrocarbon portion of this overhead product was then removed from accumulator l2 via line H and divided, part of the butenes was returned as reflux to the top of stripper 9 through line i3, the remainder of the butenes was charged to a second stage dehydrogenation unit through line H. This overhead product had the following composition:

Stream 13 or Component 14, mol per cent Butadiene 0. 26 lsobutyleue 1.93 Butane-l 46. 99 Butane-2 (low boiling) 27. B5 Butane-2 (high boiling) 20. 40 n-Butane 2. 37 (3| and heavier i0 The above example of the operation or my invention has disclosed the method and means whereby a complex stream containing principally n-butane, butene-I and butenes-2 (both low and high boiling) can be separated into n-butane and combined butenes stream by subjecting the complex hydrocarbon mixture to selective solvent extractive distillation.

Preferably the furfural in the system is maintained with a dissolved water content ranging from 1% by weight up to saturation, in accordance with the disclosure of copending application, Serial No. 438,844, filed April 13, 1942. This water enables the maintenance oi markedly lower temperatures in the bottom of fractionating-absorption column 2 and stripping column 9 Extraneous water to make up system losses is added, preferably continuously, via line I5.

I claim:

1. The process of recovering a normal butane stream suitable for recycle to a step in which normal butane is catalytically dehydrogenated to butene-1 and butene-2 and a combined butene-1 and butene-2 stream suitable as feed to a step in which normal butenes are catalytically dehydrogenated to butadiene from a principally C4 hydrocarbon mixture derived from the efiiuent of the catalytic dehydrogenation of normal butane to butene-l and butene-2, said mixture being composed principally of unconverted normal butane and butene-l and butene-2 and containing a small amount of C3 hydrocarbons and lighter which comprises subjecting said 04 hydrocarbon mixture to extractive distillation with a relatively non-volatile selective solvent which dissolves butenes in preference to butane and thereby eifecting solution of the butene content of said mixture while causing the butane content thereof to pass overhead undissolved substantially free from butene and in admixture with substantially all of the C3 hydrocarbon and lighter content, condensing said overhead and passing same into an accumulator, withdrawing from said accumulator a vaporous fraction containing most of the C3 and lighter and a liquid condensate fraction composed essentially of normal butane, refluxing the extractive distillation zone with a portion of said condensate fraction, the remainder of said condensate fraction constituting said normal butane stream suitable for recycle, reboiling the rich solvent and driving off absorbed butane in the bottom section of the extractive distillation zone, withdrawing from the bottom of the extractive distillation zone solvent enriched in butenes but substantially free of butane, and stripping said enriched solvent to recover the butenes content thereof substantially free from butane, the resulting butenes mixture being composed essentially oi butene-1 .and butene-2 and constituting said combined butene-1 and butene-2 stream suitable as feed to a step in which normal butenes are dehydrogenated to butadiene.

2. The process of recovering a normal butane stream suitable for recycle to a step in which normal butane is catalytically dehydrogenated to butene-1 and butene-2 and a combined butene-l and butene-2 stream suitable as feed to a step in which normal butenes are catalytically dehydrogenated to butadiene from a principally C4 hydrocarbon mixture derived from the eiiiuent of the catalytic dehydrogenation of normal butane to butene-1 and butene-2, said mixture being composed principally of unconverted normal butane and butene-1 and butene-2 and containing a small amount of C3 hydrocarbons and lighter which comprises subjecting said C4 hydrocarbon mixture to extractive distillation with iurfural containing at least 1% by weight of dissolved water and thereby effecting solution of the butene content of said mixture while causing the butane content thereof to pass overhead undissolved, substantially free from butene and in admixture with substantially all of the C3 hydrocarbon and lighter content, condensing said overhead and passing same into an accumulator, withdrawing from said accumulator a vaporous fraction containing most or the C3 and lighter and a liquid condensate fraction composed essentially or normal butane, refluxing the extractive distillation zone with a portion of said condensate fraction, the remainder of said condensate fraction constituting said normal butane stream suitable for recycle, reboiling the rich iuriural and driving oil absorbed butane in the bottom section I of the extraction distillation zone, withdrawing from the bottom of the extractive distillation zone furfural enriched in butenes but substantially free of butane, and stripping said enriched furfural in a separate stripping zone to recover the butenes content thereof substantially free from butane, the resulting butenes mixture being composed essentially of butene-1 and butene- 2 and constituting said combined butene-1 and butene-2 stream suitable as feed to a step in which normal butenes are dehydrogenated to butadiene.

3. The process of recovering a normal butane stream suitable for recycle to a step in which normal butane is catalytically dehydrogenated to butene-l and butene-2 and a combined butene-1 and butene-2 stream suitable as feed to a step in which normal butenes are catalytically dehydrogenated to butadiene from a principally C4 hydrocarbon mixture derived from the eilluent oi the catalytic dehydrogenation of normal butane to butene-l and butene-2, said mixture being composed principally of unconverted normal butane and butene-l and butene-2 and containing a small amount of C: hydrocarbons and lighter which comprises subjecting said C4 hydrocarbon mixture to extractive distillation with furfural containing at least 1% by weight of dissolved water and thereby effecting solution of the butene content of said mixture while causing the butane content thereof to pass overhead undissolved, substantially free from butene and in admixture with substantially all of the C3 hydrocarbon and lighter content, condensing said overhead and passing same into an accumulator, withdrawing from said accumulator a vaporous fraction containing most of the Ca and lighter and a liquid condensate fraction composed essentially of normal butane, refluxing the extractive distillation zone with a portion of said condensate fraction, the remainder of said condensate fraction constituting said normal butane stream suitable for recycle, reboiling the rich furfural and driving off absorbed butane in the bottom section of the extraction distillation zone, withdrawing from the bottom of the extractive distillation zone furfural enriched in butenes but substantially free of butane, stripping said enriched furfural in a separate stripping zone to recover the butenes content thereof substantially free from butane, introducing water into the bottom of the stripping zone to effect a lowering of the temperature therein, condensing the vapors o1 butenes and water recovered overhead from the stripping zone, causing the condensate to separate into an aqueous layer and a butenes layer, withdrawing said aqueous layer and recycling same as a source of said water introduced 7 i 8 into the bottom oi said stripping zone, withdrewin; said butenes layer, and refluxing the top 0!, REF REN S CIT D said stripping zone with a. portion of said withdrawn butenes layer, the remainder or said 1311- t gfig gg gff are mud in the tenes layer being composed essentially oi bu- 5 tene-i and butane-2 and constituting said com- UNITED STATES PATENTS bined butene-l and butane-2 stream suitable as Number Name Date ieed to a step in which normal butenes are de- 1,948,777 Young Feb. 2'7, 1934 hydrogenated to butadiene. 1,919,752 Schmidt et a] July 25, 1933 10 1,882,978 Schmidt et a1 Oct. 18, 1932 CARY R. WAGNER. 2,350,584 Buell et a] June 6, 1944 2,350,609 T-Tnnkmuth June 6, 1944* 2,2 1. 115 "Ni -"11 July 30, 1940 

